2, 4-dichlorophenoxyacetic acid compositions



W ,AWM

X 3 w. wvh/ M "cnw a R W64 m 2 7.... ...E W T 0 D T I L n A c s R s C 0 E o 3 V w r r E MW NL A W T Y l w Nav X o/o :NL R m w o .WV E mw n. o.. f B m 1 Hn/v 5 m 5 mmm E H2 G FAV .w RL m 0 FN a n F ww s r ou O .w w 4 A w-MM4w E m m mw 4m A NCH m. 4.,H2 U 5M 4 T o m M w. o. 2, www@ W m m Cwms N. l T N zr L 00N 4 o R CEE 5 Rvo 0 a/o m 20F S 0 E HEo 4o/n 8 ow m w a n, Umm zoom :RE ..5 .N QGRV m w. w 29:33 Sow SYN 25523 ww Q35 3am x ,Sv m la. w.. .M55

Dec. l2, 1950 FIGA.

UNITED STATES 'PATENT OFFICE 2,4-DICHLOROPHENOXYACETIC ACID COMPOSITION S Everett E. Gilbert, New York, N. Y., aslignonto Allied Chemical Dye Corporation, New York, N. Y., a corporation of New York Application February 1, 1949, Serial No. 73,090

This invention relates to herbicidal composi- I have discovered that, in contrast with the tions comprising 2,4-dichlorophenoxyacetic acid. very low solubility in aqueous media and common In the past 2,4-dichloropheno`xyacetlc acid organic solvents and mineral oils, 2,4-D acid may (hereinafter referred to, for Vthe purpose of be dissolved in sulfuric acid having an H1804 brevity, as 2,4-D acid?) has been used as a 5 strength of about 83% or above to produce solu- 1 herbicide in the form of a water solution of its tions having substantial dissolved content of sodium salt or its amine salt. It would be de- 2.4-D acid, i. e. about 0.2% by weight and above. sirable, if practical, to utilize 2,4-D acid as such Based on this discovery, one embodiment of my as a herbicide. However, the application of the invention comprises formation of liquid composifree acid has beenquitedifilcult due to its very l( tions comprising 2,4-D as solute in solution in low solubility in water and aqueous media (far strong sulfuric acid as solvent, which solvent has less than 0.1% by weight) and in inexpensive HzS04strengthnot less than about 83% by weight, organic solvents and mineral oils. There are the concentration of the 2,4-D solute being not serious practical diiliculties in employing meless than about 0.2% by weightbased on the solute chanlcal mixing to disperse 2,4-D acid in spray plus solvent. ,Said strong sulfuric acid solvent liquids in which the acid is insoluble. n the may suitably be an HzSO4-Hz0 phase having an other hand, if a solution of the sodium salt is HzS04-Hz0 content equivalent to that of the inacidiiied and the 2,4-D acid thereby precipitated dicated sulfuric acid strengths.

from the solution relatively large crystals of the Figure 1 represents the relation between soluprecipitated acid are obtained. Such crystals do bility 0i' 2.4-D acid 111 Strong sulfuric acid and not have the ilneness desired of a herbicide and H2804 content of said sulfuric acid at 30 C. are not suitable for spraying. Further, the It will be noted that, as H2504 content of the operation of dissolving solid sodium salt in water solvent is increased, greater amounts of 2,4-D

to form spray solutions is cumbersome and difilacid solute are soluble therein, e. g. about 0.5%

cult to carry out in commercial operation in the 2,4-D acid is soluble in sulfuric acid of 85% field. H2804 strength. Sulfuric acid solvent concentra- In order to increase the solubility of this tions as high as about 97% by weight H3804 herbicide in inexpensive organic solvents and and above. may be employed in making Solutions mineral oils, the use of co-solvents such as of 2,4-D acid in concentrated sulfuric acid. nctributyl phosphate has been proposed. However, cordingly, in its broader aspects, my invention only limited solubility increase may be obtained contemplates 97% HzSO4 and above as solvent. thereby, and, further, this method is impractical In the high concentration of HzySO4 however, sulfor large scale commercial use due to the high furic acid may tend to cause noticeable decomcost of the co-solvents employed. position of the organic solute, and, accordingly,

The action of 2,4-D acid in killing weeds is I prefer concentrate solutions having solvent relatively delayed whereas the action of sulfuric H2804 strengths not substantially above 97% by acid, a known weed killer, is very rapid. 0n the weight. As much as approximately 22% 2,4-D

other hand, the sulfuric acid is easily leached acid may be dissolved in sulfuric acid of about from the soil and its herbicidal action is thereby 97% HzSO4 content. Accordingly, a Preferred 10st, whereas 2,4-D acid, being highly insoluble 40 embodiment of my invention includes such a in water, remains in the soil a relatively long time liquid composition in which the H2504 content and its herbicidal effect is retained. The comof the sulfuric acid solvent is greater than about bination of 2,4-D acid and sulfuric acid in one 85% by weight and the 2,4-D solute content is herbicidal composition, therefore, would have the substantially in the range 0.5%-22% by weight combined desirable properties of quick kill and based on solute plus solvent. A further preferred long lasting inhibitive eifect on re-growth. v embodiment includes such a liquid composition One object of my invention is to produce a in which the H2804 content of the sulfuric acid homogeneous solution of 2,4-D acid in a solvent, is substantially in the range of 8597% H2S04 which solution may be used advantageously in by weight and the 2.4-D solute content is not making herbicide spray mixtures. A further less than 0.5%, preferably substantially in the object is to produce a dispersion of 2,4-D acid in range 0.5 %22% by weight based on solute plus liquid medium, such as aqueous sulfuric acid sulfuric acid solvent. solution, which is suitable for direct use as a In accomplishing a preferred object of the in herbicide spray. Other objects will appear herevention, I have found that mixtures of 2,4-D acid inafter. and sulfuric acid may be obtained in a form suitable for direct application as herbicide to the plants or the soil, by mixing such solutions of -.2,4-D acid in strong sulfuric acid with a material which is solvent for the H2S04 and a non-solvent 2,4-D acid, such as an aqueous medium. The 2,4-D acid is thereby precipitatedv and becomes dispersed in the solution in an extremely finely divided occulent form. lSuch ,lg disperse form system possesses enhanced herbicidal and spraying properties and accomplishes the objects previously indicated. Further, when used alone as a herbicide, sulfuric acid is known to cause deterioration of the protective tough outer coat cf the weed seeds with resultant accelerated rate of water penetration into the seed and accelerated germination. By combining 2,4-D acid with HiS04, an enhanced seed-killing action may be obtained because the 2,4-D penetrates the HzS04- softened seed coat with rapid lethal effect. Accordingly, the solutions of 2,4-D acid in strong sulfuric acid of my invention may be advantageously employed as herbicide concentrates to be subsequently diluted to produce weedand seed-killing spray mixtures.

In view of the inherent difference in nature of weed-killing properties in 2,4-D acid and H2804 mentioned above, the amounts of each of these herbicides in the spray mixture is a factor of importance in determining the plant killing properties of said mixture. rate of application in pounds per acre of 2,4-D

acid and H2S04 may depend upon the type and density of vegetation to be combatted, the degree and permanency of weed kill desired, and other factors, for most uses satisfactory results may be obtained by dispersing the 2,4-D acid over the area to be treated at a rate in the range about V2 to 12 pounds per acre. Similarly, the rate of application of H2504 may be as low as 50 pounds per acre and below and as high as 100 pounds per acre and above, but it is usual to apply sulfuric acid at the rate of about 75 pounds per acre. Accordingly, the ratio of 2,4-D acid to 100% H2504 in the spray mixture is chosen to accomplish the purpose in view, but is usually in the range approximately 1/2 to '75 (about .006) to approximately 12 to 75 (about 0.16). Due to the combined herbicidal action of sulfuric acid and 2,4-D acid, the former contributing a quick killing action, and the latter a long lasting action inhibiting regrowth of weeds and other vegetation, my invention is particularly adapted for use on a large `scale for clearing railroad tracks. In this use, 2,4-D acid may be advantageously applied at the rate of about 3A to about 8 pounds per acre,

which rate, with application of H2SO4 at 75 pounds per acre, corresponds with ratios of about 0.01 to about 0.11 pound of 2,4-D acid per pound f H2804.

It is a particular advantage of my invention that, in view of the unexpectedly high solubility oi' 2,4-D acid in strong sulfuric acid as shown in Figure 1, a concentrate solution of the former in the latter acid may be prepared which already contains the proportions of the two acids desired for the nal spray mixture. To illustrate, Figure 2 represents graphically the relation between ratio of 2,4-D acid and HzS04 desired and minimum H2804 concentration of the solvent at C. If a solution of 2,4-D acid in strong sulfuric acid having a ratio of 2,4-D acid to H2804 of 0.16 is desired, this may be obtained in sulfuric acid solvent of 94.7 weight percent H2804 content (or greater since solubility increases with percent H2804), as shown on Figure 2. On the other Although the `acess hand, a ratio as low as 0.01 may be obtained in sulfuric acid solvent of about 88 weight percent or greater H2804 content as shown by Figure 2. Ratios of 0.006 and 0.11 may be obtained in solventsof H2804 strength of about 85% and above, and ,about 93.8% and above, respectively. Simivrlarly,`for higher. lower or intermediate ratios of 2,4-D acid to I-IzSO4, there are corresponding saturation concentrations represented on Figure 2, indicating H2804 concentrations at and above which suitable concentrate solutions may exist.

It will be appreciated by those skilled in the art that solubility is generally influenced by temperature and, accordingly, that the solubility of 2,4-D acid in sulfuric acid may be appreeiably higher or lower than represented by Figure 1 accordingly as temperature is higher or lower than 30 C. If solubility is higher, minimum H2804 concentrations lower than those represented on Figure 2 may be utilized as solvent in concentrate solutions having a given ratio of 2,4-D acid to H2804. Accordingly, although particular embodiments of my invention are directed to certain prefered concentrations of HzS04 as solvent, the invention in its broader scope is not limited thereto but comprises the desired amount of 2,4-D acid solute in solution in concentrated sulfurie acid solvent of HzSO4 strength sufficient to maintain in solution said 2,4-D acid.

As previously indicated, an inspection of Figure 1 demonstrates that the solubility of 2,4-D acid in sulfuric acid increases as the H2S04 strength of the sulfuric acid increases. To facilitate the dissolving of the organic acid by the strong sulfuric acid and to minimize any possible incipient precipitation of the organic acid from the solution during storage or transportation (for example, due to change in solubility caused by temperature variations) it is preferred to employ a sulfuric acid solvent concentration which is slightly greater than the minimum required for total solution. On the other hand, in order to reduce to a minimum chemical decomposition ofthe 2,4-D acid in the concentrate, it is ordinarily preferred to employ a sulfuric acid solvent of a concentration that is not unduly higher than that necessary to maintain complete solution of the 2,4-D acid. In this way, the period during which the concentrate may be stored or shipped without excessive decomposition is lengthened. Accordingly, I prefer solvents of H2S04 concentration approximately 1/2 to 11/2% greater than saturation at 30 C., e. g. referring to Figure 1, in a solution of 4.3% 2.4-D acid in strong sulfuric acid the minimum H2SO4 concentration of solvent required is 92%, whereas I prefer concentratlons in the range approximately 921/2 to 93%% H2504.

The herbicide concentrate of my invention may be produced by adding the 2,4-D acid to the concentrated sulfuric acid while agitating the mixture at room temperature and continuing the agitation until complete solution is obtained. If desired, the 2,4-D acid may be initially dissolved in sulfuric acid of a strength higher than that finally desired for the herbicide concentrate. This will afford more rapid solution of the solute in the solvent. Thereaftenwater may be added to the mixture while continuing the agitation to reduce the strength of the solvent to a value in the range'l/z to 11/2% greater than saturation, in accordance Iwith preferred procedure as described above, or to other value desired. For instance, in making the solution of 4.3% 2,4-D acid previously referred to, the desired amount of organic acid may be ilrst dissolved in 95% H1801. and theresfterwatermaybe addedtoreducethe H2804 strength of the solvent to the ate range 956% to 935%.

Inallcaseswhenmixdngstrongsulfm'ic acid and water, precautions are taken to remove or dissipateheat of solution and thereby prevent sputtering of acid or sudden increase in pressure due to generation of steam. Suchmethode include adding a portion of the strong sulfuric acid to the water to produce a dilute acid solution, then incorporating the dilute solution with the main body of strong sulfuric acid. Alternatively, water addition may be made through a tube extending well below the surface of an agitated pool of strong sulfuric acid. Such procedures are well-known and are described, e. g. in Fairlie, "sulfuric Acid Manufacture, Reinhold (1936) at page 552. and in Miles, Manufacture of Sulfuric Acid (Contact Process) van Nostrand (1925) at page 281.

The herbicidal spray mixture will ordinarily be manufactured from the concentrate a short time before treatment of the vegetation. According to the particular herbicidal use, a liquid material which is a solvent for the sulfuric acid but a nonsolvent for the 2,4-D acid, such as an aqueous medium, is chosen to dilute the herbicide concentrate and thereby produce a spray mixture. Water is a preferred material for dilution. The concentrate is preferably added to said material while agitating. The dilution of the sulfuric acid solventby said material caus immediate precipitation of the 2.4-D acid to form a very nely divided occulent dispersion of 2,4-D acid in liquid medium, as previously indicated. When aqueous medium such as water is mixed with concentrates, herbicida] spray mixtures comprising finely divided solid occulent 2,4-D acid dispersed in aqueous solution, preferably sulfuric acid, may be obtained, said preferred mixtures having 2,4-D acid to H2804 ratios of the concentrates heretofore described. Aqueous media other than water, such as salt solutions, or acid or alkaline solutions which do not dissolve the 2,4-1) acid may be used to dilute the concentrate Solution of 2,4-D acid and thereby bring about precipitation of said acid in finely divded ilocculent form. In herbicidal work, if desired, petroleum oils or petroleum oil solutions of other herbicides may be advantageously mixed with my diluted 2A-D spray solutions, and the mixture applied to the vegetation.

Sulfuric acid is normally applied in strengths in the range of approximately 4 t0 10% when used as a herbicide. The amounts of aqueous medium employed in the dilutions of theherbicidalconcentrate according to this invention are preferably those that will produce nal sulfuric acid concentrations within this range.

The following procedures illustrate practice of my invention, the parts and percentages being by weight:

Example 1.An amount of solid 2,4-D acid in excess of saturation at 30 C. was added to and mixed with 85% sulfuric acid. 'Ihe mixture was agitated at 30 C. until saturation was obtained. Excess undissolved 2,4-D acid was then removed from the solution. which contained 2,4-D acid solute in solution in sulfuric acid Solvent. The solvent contained 85% H2804 and 15% H20, and the solution contained 0.5% 2,4-D acid based on solute plus solvent. The weight proportion of 2.4-D acid to HzSO4 in said solution was about 0.006. In this manner saturated homogeneous solutionsof 2.4-1) acid in strong sulfuric acid of the following compositions were obtained:

Per cent o! 2 4-D acid Per cent Per cent Ratio 2.4-D

tmc on mso. m ne mo in the ad zo solute plus solvent solvent H1804 solvent 0. 5 85 i5 0. 01B 4. 3 92 8 0. D5 10:3 94 0 0. 115 14. 8 05 5 0. 173 2l. 8 0d. 8 3. 2

Example 2.--10 parts of 2,4-D acid were added to 190 parts of 96% HeSO4 sulfuric acid and the mixture agitated at about 30 C. until all of the 2,4-D acid had dissolved. The resulting mixture was a homogeneous solution containing 2,4-D acid solute dissolved in sulfuric acid solvent. 'I'he solvent contained 96% H2804 and 4% H2O and the solution contained 5% 2,4-D acid based on solute plus solvent. I'he ratio of 2,4-D to H2804 was about 0.055. This solution was poured into 2400 parts by weight of water while vigorously stirring said water. The mixture obtained contained solid 2,4-D acid precipitated in extremely nely divided flocculent form suspended in a solution of H2804 in water of about '1% strength. 'I'his mixture was suitable for direct use as a herbicide spray. Upon standing for one day, the 2,4-D acid remained suspended in the liquid in light cottony flocks.

By contrast. an amount of 2,4-D sodium salt equivalent to said 2,4-D acid, dissolved in 2400 parts of water and acidified with vigorous stirring produced a 2,4-D acid precipitate which had a noticeable crystalline structure, which crystals occupied a fraction of the apparent volume of the cottony flocks produced by addition of the 2,4-D-su1furic acid solution to water as described above.

Example 3.-10 parts of 2,4-D acid were added to 920 parts of 95.5% H1804 sulfuric acid and the mixture was agitated at about 50 C. until complete solution was obtained. While continuing the agitation, 70 parts of water were added slowly to the mixture. This reduced the acid concentration of the solvent to about 89% H1804. No precipitation of 2,4-D acid solute occurred. 'I'he resulting solution containing solvent of about 89% HzSOi, 11% H20 composition, and the 2,4-D content of the solution was 1.0% based on solute plus solvent.

I claim:

1. A liquid composition 2,4-dichlorophenoxyacetic acid as solute in solution in strong sulfuric acid as solvent, said solvent having an H2804 strength not less than about by weight, the concentration of said solute being not less than about 0.5% by weight based on said solute plus solvent.

2. A liquid composition of matter comprising 2,4-dichlorophenoxyacetic acid as solute in solution in an H2S04-Hi0 an H2SO4-Ha0 content equivalent to that of sulfurie acid substantially in the range of it-97% H2804 strength, the concentration of said solute being substantially in the range of 0.5%-22% by eight based on said solute plus HaSO4-H20 con- 3. A liquid composition of matter. adaptable for use as a herbicidal concentrate, com 2,4-dlchlorophencxyacetic acid as solute in solution in strong sulfuric acid as solvent. said aolof matter comprising phase, said phase having 7 vent having an H2804 strength not less than about 85% by weight, and the weight ratio of said solute to said H250x being substantially in the range of 0.0060.16.

4. A liquid composition o! matter. adaptable for use as a herbicidal concentrate, comprising furie acid in the range of 8897% HzSO4 strength,

and the weight ratio of said solute to said H2504 being substantially in the range of 0.01-0.11.

6. A homogeneous solution consisting of 2,4-dichlorophenoxyacetic acid as solute in solution in an H2SO4-H2O phase, said phase having an H2S04-H20 content equivalent to that of sulfuric acid in the range of atl-97% H2804 strength, and

the weight ratio of said solute to said H2804 being substantially in the range of 0.0060.16.

7. The method of producing 2,4-dichlorophenoxyacetic acid in finely subdivided fiocculent form dispersed in liquid medium which comprises mixing a solution of 2,4-dichlorophenoxyacetic acid in strong sulfuric acid with a liquid which is a solvent for said sulfuric acid but is a non-solvent for said 2,4-dichlorophenoxyacetic acid. whereby said 2,4-dichlorophenoxyacetic acid is precipitated in a finely divided ilocculent form in liquid medium.

8. A method of producing a herbicidal spray mixture which comprises dissolving 2,4-dichlorophenoxyacetie acid as solute in strong sulfuric acid of HgSO4 content substantially in the range of 88-97 H2S04 by weight, the weight ratio of said solute to said H2504 in the solution so formed beingin the range approximately 0.01 to approximately 0.11, and thereafter incorporating said solution with aqueous medium while agitating said aqueous medium, the amount of said medium being such that the H2804 concentration 'is reduced to the range approximately 4 to 10% by weight, thereby to obtain a herbicidal spray mixture having 2,4-dichlorophenoxyacetic acid dispersed therein in finely subdivided iiocculent form.

f EVERE'I'I E. GILBERT.

REFERENCES CITED The following references are of record in the ille of this patent: y

UNITED STATES PATENTS 

1. A LIQUID COMPOSITION OF MATTER COMPRISING 2,4-DICHLOROPHENOXYACETIC ACID AS SOLUTE IN SOLUTION IN STRONG SULFURIC ACID AS SOLVENT, SAID SOLVENT HAVING AN H2SO4 STRENGTH NOT LESS THAN ABOUT 85% BY WEIGHT, THE CONCENTRATION OF SAID SOLUTE BEING NOT LESS THAN ABOUT 0.5% BY WEIGHT BASED ON SAID SOLUTE PLUS SOLVENT. 